Quick way to test: put the pull valve on the whistle and try to mouth-blow through it. If you can't "blow enough" the valve is too small or too restrictive, and you'll need to go to a larger size.
Use a can of coffee (or grapefruit juice or the like) for a pressure tank -- my 1979 Lincoln did for vacuum! You can cut small holes to remove the contents and wash the inside out, then solder flanges or fittings from a hardware store on. I'd make some kind of overpressure valve protection even if the compressor is small. There are also setups for using a small compressor with automobile air horns or adjustable air-bag suspension that have proper accumulator tanks. Run the compressor to keep the tank charged, and as Randy said, gate the output from the tank with the pull valve.
(Incidentally, where the air blows into the whistle structure might be having some effect -- see if using a longer piece of tube or pipe between the valve and the whistle changes anything.)
Definitely a volume issue. Plenty of pressure from the compressor - even the blow gun test wasn't bery good. Low mouth pressure but high lung volume, and the low pressure but also very high volume from the air mattress blower worked fine.
To make it blow off the air compressor, you're going to need an accumulator chamber before the whistle, and then I suspect have to gate that, rather than the supply air. Even then, the length of blast it will do will be limited by the size of the expansion chamber.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I suspect it is the volume of air rather than the pressure. The tiny "pull valve" simply may not have the internal clearance (orifice size) to allow a sufficient volume of air needed to blow the whistle.
I had some lever valves of up to one inch pipe size. I think you need to find a lever valve with at least a 1/4 or 3/8" pipe diameter.
They get crazy money for brass whistle valves of any size these days. You can get the "blow-gun" type valve fairly reasonably.
https://www.toolpan.com/Milton-Industries-151--Blow-Gun-Control-Valve_p_23115.html?gclid=Cj0KCQiArvX_BRCyARIsAKsnTxPUGVqSPsJjd6XMO2_bMj79s2NoBqJdy2jLgBesVEC0jUr-yY3LE0MaAm2WEALw_wcB
There are other vendors, the above is just an example.
Good Luck, Ed
I made a video of my tests but the issue is that the whistle sounds great if I blow it under my power. It works if I use an electric mattress pump. It even worked when I used just a compressed air blow gun. However, when I put a hand pull valve on it it doesn't work. I've tested changing the regulator pressure as well and nothing works. I'm needing this for a project I'm building for my son so I appreciate any help! thanks!